In many applications of an electric motor, it is common for the motor to suddenly encounter a mechanical load which is beyond its torque producing capability. This condition necessitates the incorporation of some external apparatus for either removing a portion of the motor load, terminating operation of the motor or in some way increasing the torque applied to the load. In some motor uses it is possible to store mechanical energy for use in these high torque situations by coupling such devices as flywheels or spring mechanisms to the motor or its load. In other motor uses it is necessary to provide a motor having torque output which is in excess of that normally required by the load in order that the expected but infrequent need for increased torque be accommodated. Each of these solutions obviously has undesirable features.
Although many examples of motor loads which involve a sudden imposition of high load torque are to be found, it is likely that none of these examples equals the torque needed when unusual raw materials are introduced into a stationary machine of the crushing and grinding type. The absence of stored kinetic energy or flywheel effect and the impossibility of impacting engagement between the raw material and the working member of the machine in this situation profoundly increases the torque required of the driving motor; indeed the presence of a flywheel would actually detract from the ability of the motor to process the raw material in such cases since the torque rerquired to accelerate the flywheel would add to the torque required for working the unusual raw material.
Frequently encountered examples of crushing and grinding equipment which are subject to this type of load include hammer mills, rock crushers, tree limb choppers, wood hogs and waste disposers. The waste disposer machine is a particularly exacting example of a sudden high torque motor load since popular demand for these machines necessitates that they have small physical size, low initial cost, long unattended operating life and comminuted material output which is limited to small particle sizes.
Despite the increasing acceptance of waste disposer equipment as a desirable element of kitchen operations, no single disposer design has been forthcoming to fully satisfy these desired properties. In particular, the need for long trouble-free operating life, small output particle size, low cost, and small physical dimensions appear to almost mutually exclude one another and necessitate design compromise in machines built according to presently available technology. An example of this compromise is to be found in the trade-off between output particle size, long unattended operating life and low original cost, since it is found that disposers having small clearance between operating members (as is required to produce small output particle size) are also most subject to jamming so as to need professional maintenance attention. The low initial cost requirement, of course, precludes the use of a driving motor having excessively large reserve torque capability.
The present invention relates to an apparatus and method by which a waste disposer, a crushing and grinding apparatus, or other motor driven machine can better meet the above requirements. In particular, the present invention relates to apparatus for increasing the torque produced by an alternating current motor and changing this torque into a pulsating form which has been found particularly suited to overcoming the jamming problems encountered in crushing and grinding equipment.